Add the olive oil and 2 tablespoons of the butter to a small saucepan over medium heat. Add the onion and cook for 2-3 minutes. Add the garlic, Clam Base, oregano, and red pepper and cook for 30 seconds more. Add the heavy cream, bring to a boil, reduce the heat and simmer for 5-6 minutes. Stir in the parsley and remaining butter and pour the sauce over the steamed mussels.

Add 2 inches of water to a large stockpot and bring to a boil. Add the mussels to the water. Cover and steam for 4-5 minutes or until the mussels have opened. Remove the opened mussels to a serving bowl. Discard any unopened mussels.